The real reason for using BSP for that diameter is TPI. Given the diameter, in BSW the nearest size would be about 7 tpi, in BSF it would around 9 tpi, so it makes sense to go to BSP and use a standard pipe diameter which give 14 tpi, much more sensible.
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Richard
1943 Bedford QLD lorry - 1941 BSA WM20 m/cycle - 1943 Daimler Scout Car Mk2
Member of MVT, IMPS, MVG of NSW, KVE and AMVCS
KVE President & KVE News Editor
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